Method for treating solid waste with an organic fraction

ABSTRACT

The present invention concerns a method for treating solid waste with an organic fraction. A slurry ( 4 ) of the waste ( 1 ) diluted with water ( 3 ) is sieved, at least by means of a sieving device ( 5 ) which lets pieces through whose dimension in at least one direction, and preferably in at least two standing directions, is situated between 2 and 20 mm, after which, from the slurry ( 7 ) which has passed through, a part of the ferrous metals ( 8 ) which are present in the waste ( 1 ) is removed from said waste by means of magnets, and the slurry ( 7 ) is finally dewatered.

[0001] The present invention concerns a method for treating solid wastewith an organic fraction, according to which method the waste is sievedwhile wet.

[0002] In the case of a selected collection of domestic waste, theorganic fraction, provided it does not contain any major amounts ofheavy metals, can be biologically treated into a high-grade compost.

[0003] The remaining residual waste, also called grey waste, stillcontains an amount of organic material and materials which can berecycled. This waste is burnt or dumped, which is relatively expensiveand not environmentally friendly.

[0004] In some cases there is no selected collection of the domesticwaste. This mixed domestic waste, which still contains a large fractionof organic material, is treated in the same manner as theabove-mentioned residual waste.

[0005] Installations have been built to recycle the fractions of theabove-mentioned residual waste and mixed waste which are suitable to berecycled. A thorough pre-selection was hereby carried out, followed by abiological treatment to obtain compost.

[0006] The major problem thereby is the quality of the end products,especially the presence of heavy metals, in particular in the compost.

[0007] Up to now, the selection has not been sufficient to produce largeamounts of marketable end products with a stabilised organic fractionhaving a low proportion of heavy metals.

[0008] For several years, also dry selection of residual waste and mixeddomestic waste has been applied by means of sieves, magnets erectedabove conveyor belts, air selectors, etc. The quality of the endproducts is such that they are not suitable for re-use or recycling. Thedry selection techniques are so inefficient that in many countries, aseparate collection of recyclable waste and biowaste has been introducedso as to obtain separate flows and so as to obtain products of anacceptable quality thanks to selection and treatment.

[0009] According to known methods for treating grey and mixed domesticwaste or other solid waste with an organic fraction, the waste isbiologically treated by making use of aerobic composting. The waste isstabilised and dried while being composted, after which ferrous metalsand a fine sand fraction are recycled. The other major part of the drysubstance of the waste has to be burnt, which is expensive.

[0010] Wet selection offers interesting prospects, in particular forresidual waste, mixed waste with an organic fraction originating fromdomestic waste, and industrial waste which is comparable to domesticwaste, which have been pre-selected in a conventional manner.

[0011] The removal of ferrous metals by means of magnets which are builtin in waste conveyor devices or which hang over them, is restricted tolarge parts which are attracted by the magnets. A large number ofsmaller particles remains embedded in the waste.

[0012] Few devices for the treatment of solid domestic waste reduce theorganic fraction to less than 20 mm, since the costs therefor rise fastwith the degree of reduction.

[0013] Wet selection offers the possibility to loosen the particles fromone another by adding large amounts of water, as a result of which thedifferent components become accessible for selection.

[0014] However, the application of wet selection methods has beenrestricted up to now, as they usually produce strongly contaminatedwaste water, whose further treatment is expensive.

[0015] In aerobic composting installations, in which a solid substancecontent of about 50% is ideal, only a small amount of water can be addedbefore an excess of waste water is produced which cannot be internallyrecycled in the composting device.

[0016] Methods whereby use is made of an anaerobic fermentation offermore possibilities for a wet selection, since said fermentation takesplace in more humid circumstances than the aerobic composting, and anexcess of waste water often cannot be avoided, so that a device for thewater removal and the treatment of waste water is in any case required.

[0017] Anaerobic fermentation of waste can take place by means of dryfermentation, with over 15% dry substance in the reactor, as well as bymeans of wet fermentation with less than 15% dry substance in thereactor.

[0018] Methods whereby use is made of the wet fermentation for thetreatment of waste which has been selected at the source, are designedto remove pollutants such as floating materials and heavy substancesbefore the wet fermentation takes place, such that a fraction isobtained which is rich of organic material and poor of pollutants, asdescribed for example in EP-A-0.520.172

[0019] According to this last method, solid components are separatedbefore the ferrous metals are separated from the dry waste by means ofmagnets and after water has been added, after which the residue issubjected to the wet fermentation.

[0020] A device which is suitable for the wet selection of heavyaggregates from mixed domestic waste or similar waste is described inEP-A-0.228.724. Stones, ceramic materials, batteries and heavy lumps,including some lumps of synthetic material, are separated by means of aseparating tank filled with water, before the biological treatment takesplace, so as to obtain a compost with few heavy components.

[0021] The treatment of mixed solid domestic waste may also include awet pre-treatment into a pulp or a wet sieving, followed by a separationby a hydrocyclone.

[0022] According to such a known method, the waste with an organicfraction is pre-treated first in a dry selection device, where acombustible fraction, ferrous metals and other materials are recycled.

[0023] Mixed organic waste is separated by means of sieving, and afterhaving been diluted with water, it is supplied to hydrocyclones, wherethe large inert components are separated.

[0024] The remaining fine organic material is separated by means of asieve and then directed to a hydrocyclone again, where the sand fractionis removed. This last fraction is dewatered.

[0025] The rough organic fraction which is stopped by theabove-mentioned sieve, is mixed with synthetic materials and otherundesirable pieces which have already been separated and reduced in acrushing mill.

[0026] The remaining organic fraction is finally subjected to afermentation.

[0027] As the separation takes place before the fermentation, the wateris strongly contaminated, however, since all soluble components, such asorganic fatty acids, sugars, etc. are present in the waste. Moreover,large quantities of water are required, and the separation isinefficient due to the heterogeneous character of the waste, which stillcontains the sticky and smelly organic substances which will have to bedegraded in the subsequent fermentation or composting.

[0028] In fact, only sand is obtained as a recyclable material.

[0029] According to other known methods, the materials are separatedafter the fermentation or composting of the organic fraction. U.S. Pat.No. 4,079,837 describes a method for the recycling of recyclablematerials after a fragmentation by means of thermal explosivedecompression, followed by a biodegradation in a composting treatment.The fragmented and composted waste residue is separated into severalfractions by means of conventional dry sieving and separation by air.Synthetic material is separated by means of floatation.

[0030] Fine sand, clay and other inert materials can be separated duringthe treatment after the hydrolysis in a two-phase fermentation asdescribed in EP-A-0.142.873.

[0031] All the above-mentioned methods with wet treatments produce acompost of low quality and secondary materials, most of which containtoo many heavy metals, especially if domestic residual waste or mixedwaste is taken as a basis.

[0032] The positive effect of the biological treatment is often mainlyrestricted to the recycling of energy in the form of biogas and theproduction of a highly calorific fraction at the time of the dryselection during the pre-treatment.

[0033] The invention aims a method for the treatment of solid waste withan organic fraction which does not have the above-mentioneddisadvantages and which makes it possible to obtain end products whichdo not contain large proportions of heavy metals.

[0034] This aim is reached according to the invention in that a slurryof the waste which has been diluted with water is sieved, at least bymeans of a sieving device which lets pieces through having a dimensionin at least one direction, and preferably in at least two standingdirections, which is situated between 2 and 20 mm, after which, from theslurry which has passed through, a part of the ferrous metals which arepresent in the waste is removed from said waste by means of magnets, andthe slurry is finally dewatered.

[0035] It was found that the heavy metals usually adhere to ferrousmetals, so that thanks to the removal of the latter, the concentrationon the rest of the waste is reduced.

[0036] The diluted slurry can be produced in a separate stage whichtakes place just before the sieving or even during the sieving. However,the dilution into a slurry can also take place during a pre-treatment,for example during an anaerobic fermentation or hydrolysis when the drysubstance content is low.

[0037] Preferably, waste is sieved which has been diluted into a slurrywith a dry substance content of less than 10%.

[0038] Between the sieving and the removal of the ferrous metals, theabove-mentioned slurry can be aerated.

[0039] After the removal of the ferrous metals, the sand can be removedfrom the slurry, for example by means of at least one hydrocyclone, andthe fibrous material can be removed from it, for example by sieving withthe help of at least one sieving device which lets pieces through whosedimension in at least one direction, and preferably in at least twostanding directions, is smaller than 2 mm.

[0040] Preferably, after the separation of the ferrous metals, and afterthe water has been removed, the dewatered slurry is subjected to abiological treatment, in particular composting.

[0041] In order to better explain the characteristics of the invention,the following preferred embodiments of a method for the treatment ofsolid waste containing an organic fraction according to the inventionare described as an example only without being limitative in any way,with reference to the accompanying drawings, in which:

[0042]FIG. 1 represents a block diagram of a device for applying themethod according to the invention;

[0043]FIG. 2 represents the part of the device in which ferrous metalsare separated by means of magnets into greater detail, but stillschematically;

[0044] FIGS. 3 to 5 represent block diagrams analogous to the one inFIG. 1, of devices for the application of the method according to theinvention, but with reference to other embodiments of the method.

[0045] For the treatment according to the invention of solid waste 1containing an organic fraction, as represented in FIG. 1, a dilutionwith water 3 first takes place in a dilution device 2 until a slurry isobtained containing for example maximum 10 of dry substance.

[0046] The waste 1 to be treated may be the part containing organicmaterial which has been obtained thanks to the dry selection of mixeddomestic waste, industrial waste which is comparable to domestic wasteor residual waste, or it may originate from a composting device or afermentation device.

[0047] If the waste originates from an anaerobic fermentation orhydrolysis, the dilution can take place during this pre-treatment. Thefermentation or hydrolysis can take place with less than 10% of drysubstance. The dilution device then consists of the anaerobicfermentation tank or the hydrolysis tank.

[0048] The obtained slurry 4, in which the solid substance is stronglydispersed, is subsequently sieved in a sieving device 5 having suchopenings that pieces can go through it having a dimension in at leastone direction, and preferably in at least two directions, which issituated between 2 and 20 mm. This sieving device 5 has for exampleround openings with a diameter of 20 mm or square openings with a sideof 20 mm, but all sorts of shapes are possible of course.

[0049] If the slurry 4 contains clods, it is possible to provide amechanical action during the dilution or sieving, for example amechanical mixing or stirring, so that the clods break as a result offriction or such.

[0050] In order to speed up the sieving, one or several strong waterjets can be directed onto the slurry 4, whereby these water jets pressthe slurry through the sieving device and can make the clods in theslurry disintegrate further.

[0051] It is even possible to obtain the dilution of the waste 1 bymeans of one or several water jets, such that the dilution and thesieving take place in one and the same direction, which is a combinationof the dilution device 2 and the sieving device 5.

[0052] The rough fraction 6 is discharged for further treatment. Fromthe fine slurry 7 which goes through the sieving device 5 and whichcontains particles of 20 mm at the most, the largest part of the ferrousmetals 8 is separated in a subsequent stage by means of a magnetictreatment with one or several magnets 9.

[0053] To this end, the slurry 7 can be guided through a pipe in which amagnet 9, for example in the shape of a grid, is erected between twostop valves.

[0054] From time to time, the magnet 9 with the ferrous metals 8adhering onto it, is taken out of the pipe. The ferrous metals 8adhering to the magnet 9 are removed before the magnet 9 is put intoplace again.

[0055] Instead of being placed directly in the slurry 7, the magnet 9can grasp over the pipe.

[0056] Both embodiments require the separation to be temporarily stoppedso as to remove the ferrous metals 8.

[0057] How it is possible to work continuously is illustrated in FIG. 2.

[0058] The slurry 7 is guided through an ingoing pipe 10 which branchesoff in two pipes 11 and 12 onto which are mounted removable magnets 9,for example electromagnets, which then join one another again in anoutgoing pipe 13.

[0059] Upstream of the magnets 9 is provided a stop valve 14 in eachpipe 11 and 12, whereas downstream of these magnets 9 is also erected astop valve 15 in each pipe 11 and 12.

[0060] Between each stop valve 14 and the magnet 9 is connected a watersupply line 16 onto each pipe 11 and 12, whereas downstream of each stopvalve 15 is connected a discharge pipe 18 for ferrous metals 8 which canbe closed off by a stop valve 17.

[0061] During the normal operation, the stop valves 14 and 15 are openin either one of the pipes 11 or 12, for example the pipe 11. The otherstop valves 14 and 15 and the stop valves 17 are closed, and no water issupplied via the water supply lines 16.

[0062] Ferrous metals 8 found in the slurry 7 are retained in the pipe11 which is in use by means of the magnet 9 which is situated in theimmediate vicinity of the slurry 7.

[0063] After a certain length of time, the stop valves 14 and 15 in theother pipe 12 are opened, whereas the stop valves 14 and 15 in the pipe11 are closed, and the stop valve 17 in the discharge pipe 18 connectedonto it is opened. The magnet 9 is removed from the pipe 11, so that theferrous metals 8 are no longer retained. By injecting water via thewater supply lines 16, these ferrous metals 8 are discharged from thepipe 11, via the open stop valve 17 and the discharge pipe 18.

[0064] Then, the water supply is stopped and the above-mentioned stopvalve 17 is closed again. The electromagnet 9 is put in its initialposition again on the pipe 11.

[0065] In the meantime, ferrous metals 8 have been removed from theslurry 7 in the other pipe 12 by the other electromagnet 9.

[0066] The removal of the ferrous metals 8 from this pipe 12 takes placein the same manner as described above for pipe 11, but the stop valves14 and 15 in this pipe 11 are first opened again, so that the ferrousmetals 8 can now be separated again in the first pipe 11.

[0067] Thus, both pipes 11 and 12 are alternately used for the removalof the ferrous metals 8.

[0068] In all these embodiments, the slurry 19 from which the ferrousmetals 8 have been removed in a magnetic manner, is discharged to adewatering device 20, for example a centrifuge, in which they aredewatered. The separated water 3 with a solid substance content of lessthan 5% is recycled to the dilution device 2.

[0069] This dewatering can take place in two or several steps, wherebythe last step is a mechanical dewatering and a preceding step issedimentation or floatation, either or not with the addition offlocculation means.

[0070] The dewatered fraction 21 has a low concentration of heavymetals, since the latter are partly fixed on the ferrous metals 8 andhave been retained together with the latter by the magnets 9. Thisfraction 21 can be dumped or for example composted.

[0071] Between the magnetic removal of the ferrous metals 8 and thedewatering, the slurry 19 can be subjected to an aerobic treatment oroxidation, for example it can be aerated in an aerator 22, in which airis blown in via a pipe 23, as represented in FIG. 3.

[0072] This embodiment further differs from the above-describedembodiment in that the rough fraction 6 is guided from the sieving to aseparation device 24, for example a sedimentation tank, where thefraction 25, consisting of the organic and woody fraction, as well asthe synthetic fraction, is separated from the inert fraction 26.

[0073] The dewatered fraction 21 of the dewatering device 20 isbiologically treated, for example in the composting device 27, where itis processed into compost 28.

[0074] Instead of a composting device, a fermentation tank can be used,provided the waste 1 has not been fermented yet in an anaerobic manner.

[0075] The removal of the ferrous metals 8 in the above-described mannermay be sufficient for some applications, but for most waste with anorganic fraction, the proportion of heavy metals in the obtained endfractions remains too large.

[0076] In order to avoid this, one proceeds as will be illustrated bymeans of the device represented in FIG. 4. This device differs from thedevice according to FIG. 3 in that, between the magnetic separation ofthe ferrous metals and the aerator 22, or the dewatering device 20 ifthis aerator 22 is omitted, the following other devices are present.

[0077] After the magnet 9 is erected a separator 29 working on the basisof rotational flows in which the non-ferrous metals 30 are separatedfrom the slurry 19.

[0078] Next is erected a sand separator 32, for example a hydrocyclone,in which a sand fraction 33 is separated from the remaining slurry 31.From this sand fraction 33 can be removed remaining organic componentsand other undesirable components in a second sand separator 34, forexample a second hydrocyclone, in order to reduce the proportion ofsolid organic components, so that a rather pure and re-usable sandfraction 35 is obtained.

[0079] The organic slurry 36 which is separated in this second sandseparator 34 is combined with the slurry 37, which is also rich oforganic components, originating from the sand separator 32, and theresulting slurry 38 is then finely sieved in the sieving device 39 withopenings which can let particles through whose dimension, at least inone direction, and preferably in at least two standing directions, issmaller than or equal to 2 mm. This sieving device 39 has for exampleround openings with a diameter of 2 mm or square openings with a side of2 mm.

[0080] Thanks to the sieving device 39 is obtained a fine slurry 40 onthe one hand, and a fibrous fraction 41 on the other hand. The latterfraction is supplied to a third sieving device 42, for example a basketsieve or a rotating sieve, in which the fibres 43 having a lowconcentration of heavy metals are separated from a fraction 44containing the synthetic materials, metals and pollutants bond withthem, and other undesirable materials, such by means of sieving.

[0081] This third sieving device 42 only lets particles through of whichat least one dimension is smaller than 500 micrometer, and it has forexample round openings with a diameter smaller than 500 micrometer orsquare openings with a side smaller than 500 micrometer. In this case,the above-mentioned dimension of the openings of the first sievingdevice 5 is preferably smaller than 5 mm and the dimension of the secondsieving device 39 is smaller than 1 mm.

[0082] The fine slurry 40, having a particle size of less than 2 mm,containing the largest part of the remaining heavy metals which did notadhere to the ferrous metals 8 and which have not been separated by theseparator 29, can be directly dewatered in the dewatering device 20 and,depending on the initial concentration of heavy metals and the standardrequirements for the compost 28, can be composted in the compostingdevice 27.

[0083] Onto this composting device can be added the sand fraction 33, orpreferably the sand fraction 35 and/or the fibrous fraction 41, orpreferably the fibres 43, as is represented by the dashed line in FIG.4. From these fractions or fibres can possibly also be removed smallamounts of remaining heavy metals in a chemical manner, for example bymeans of a chelator.

[0084] The fibres 43 offer the structure material which is required forthe aerobic treatment, whereas the slurry 40 supplies the nitrogen whichis necessary for the biological activity.

[0085] The compost 28 is a good compost which is relatively free ofpollutants such as synthetic materials and glass.

[0086] As already mentioned, an aeration or in other words an oxidationof the slurry 40 can take place before the dewatering, for example for0.1 to 72 hours. Onto the aerator 22 can be added oxidising agents. Saidoxidation promotes the dewatering.

[0087] This aeration or oxidation can, as represented in FIG. 4, bepreceded by a settling caused by the gravitational force or bysedimentation, and simultaneously by floatation in a sedimentationdevice 45, where the slurry 40 is thickened, so that less aeration anddewatering is required. The discharged water 45A is added to the water 3for the dilution device 2.

[0088] When the above-described method was applied, the followingresults were obtained, represented in this table: A B C D E F Organic 80.8 78 94.4 50 50 volatile substances (%) Heavy metals (ppm on drysubstance) As <5 1.8 2.6 1.6 6.1 — Cd <0.5 <0.5 0.8 <0.5 1.5 1.4 Cr 6048 52 21 136 36 Cu 100 93 74 29 190 80 Hg 0.1 0.8 1.1 0.7 2.8 — Pb 55119 91 27 225 90 Ni 16 26 25 10 63 18 Zn 310 190 480 170 824 250

[0089] Whereby

[0090] A is the sand fraction 33 after the sand separator 32,

[0091] B is the sand fraction 35 after the second sand separator 34,

[0092] C is the fibrous fraction 41 after the fine sieving in the sieve39,

[0093] D are the fibres 43,

[0094] E is the dewatered fraction 21,

[0095] F is the slurry after an extra purification with a chelator.

[0096] A compost of even better quality and a smaller water consumptioncan be obtained with the device represented in FIG. 5. In so far as thisdevice corresponds to the one according to FIG. 4, identical fittingsand flows have been indicated with the same reference figures.

[0097] The waste 1 is first diluted in the dilution device 2 and thensieved by the sieving device 5. The rough fraction 6 is separated in theseparating device 24, for example a sedimentation tank, into a heavyfraction, namely the inert fraction 26 containing glass and stones andforming for example the sediment, and an organic, woody and syntheticfraction 25 which forms for example the floating fraction.

[0098] The latter is dewatered in a dewatering device 46. The separatedwater 47 is added to the slurry 7, before it undergoes the magnetictreatment.

[0099] There is for example no separation by means of a separator 29,although it would be possible, but both the slurry 38 of the sandseparator 32 and the slurry 40 of the fine sieve are magneticallytreated by means of a magnet 48, 49 respectively, similar to theabove-described magnet 9.

[0100] Before or after each magnet 9, 48 and 49 can be erected aseparator 29 working on the basis of rotational flows to remove thenon-ferrous metals. For clarity's sake, such a separator 29 is onlyrepresented in FIG. 4.

[0101] Before the sand fraction 33 of the sand separator 32 is suppliedto the second sand separator 34 in order to reduce the proportion oforganic solid substances, it is first dewatered in a dewatering device50, the water 51 of which is added to the slurry 37, and subsequentlythe solid sand fraction is mixed with water 53 originating from aphysical/chemical water treatment in a tank 54 in a mixer 52.

[0102] Also after the second sand separator 34, the sand fraction 35 isdewatered in a dewatering device 55 of which the water 56 is collectedin the tank 54. The organic slurry 36 of the second sand separator 34 isadded to the organic slurry 37 of the sand separator 33, and togetherthey are subjected to the treatment by the magnet 48 which separatessome extra ferrous metals 48 A, before being finely sieved by the sieve39.

[0103] According to a variant, the dewatering devices 50 and 55 can bereplaced by sedimentation tanks, whereby the sediment is the sandfraction, or by other appropriate systems.

[0104] The fibrous fraction 41, before being sieved again in the sievingdevice 42, is magnetically treated as a slurry by a wet magnet 57,whereby an extra quantity of dispersed ferrous metal 58 is removed fromit. The resulting slurry 59 is dewatered in the dewatering device 60 andmixed in a mixer 61 with water 53 coming from the tank 54.

[0105] The fibres 43 which have been separated from the syntheticmaterials, the metals bond with these and other products by means of thesieving device 42 or another separation device are dewatered in thedewatering device 62, of which the water 63 is collected in the tank 54to be for example physicochemically treated.

[0106] Thanks to this water treatment in the tank 54 and the use ofwater from this tank 54 for separating sand in the second sand separator34 and for diluting the fibrous fraction 41, the consumption of freshwater is minimised.

[0107] A possible excess of the water 3 which is sent from thedewatering device 20 to the dilution device 2 can also be treated in thetank 54. If there is too much treated and thus purified water, this canbe discharged.

[0108] From the slurry 40 which has passed through the fine sieve 39,onto which the water 64 of the dewatering device 60 has been added, areremoved the final fine rests of ferrous metals 49A with the magnet 49,after which the slurry is dewatered in the dewatering device 20.

[0109] Before the dewatered fraction 21 is sent to the composting device27, possibly together with the purified and dewatered sand fraction 35and the dewatered fibres 43, it can be mixed with a regenerated watersolution 72 with active chelators, and it can be dispersed by means ofmixing or friction in the device 65.

[0110] Afterwards, the fraction 21 can be further treated in a reactor66, onto which are added chelators 67 which are preferablybiodegradable, for example as described in EP-A-0.267.653, so as tosolve an additional part of heavy metals which have not been removedtogether with the ferrous metals, and so as to remove them from thesolid matter at the time of the dewatering in the dewatering device 68.

[0111] The metals 71 are separated from the water 69 of the dewateringdevice 68 in a regeneration unit 70. The regenerated water solution 72is added to the device 65, and is thus re-used for the removal of theheavy metals in the reactor 66.

[0112] In the last described embodiment according to FIG. 5, the use offresh water is minimal and the costs for treating the excess of waterfor the treatments are limited.

[0113] The invention is by no means limited to the above-describedembodiments represented in the accompanying drawings; on the contrary,such a method for the treatment of solid waste containing an organicfraction can be made in all sorts of variants while still remainingwithin the scope of the invention.

1. Method for treating solid waste with an organic fraction, accordingto which method the waste (1) is sieved while wet, characterised in thata slurry (4) of the waste (1) which has been diluted with water (3) issieved, at east by means of a sieving device (5) which lets piecesthrough having a dimension in at least one direction, and preferably inat least two standing directions, which is situated between 2 and 20 mm,after which, from the slurry (7) which has passed through, a part of theferrous metals (8) which are present in the waste (1) is removed fromsaid waste by means of magnets, and the slurry (7) is finally dewatered.2. Method according to claim 1, characterised in that diluted slurry (4)is produced in a separate stage which takes place right before thesieving or during the sieving itself.
 3. Method according to claim 1,characterised in that the dilution into a slurry (4) already takes placeduring a pre-treatment, for example during an anaerobic fermentation orhydrolysis when the dry substance content is low.
 4. Method according toany of the preceding claims, characterised in that waste (1) is sievedwhich has been diluted into a slurry with a dry substance content ofless than 10%.
 5. Method according to any of the preceding claims,characterised in that the water (3) of the dewatering process isrecycled and is used for the dilution.
 6. Method according to any of thepreceding claims, characterised in that the rough fraction which isretained during the sieving by means of a sieving device (5) isseparated in a separation device (24), namely into an inert fraction(26) and a fraction (25) which is possibly dewatered in a waterseparator (46) of which the water (47) is added to the slurry (7) againafter the sieving.
 7. Method according to any of the preceding claims,characterised in that, apart from the removal of the ferrous metals (8),also the non-ferrous metals (30) are removed, for example by means of aseparator (29) working on the basis of rotational flows.
 8. Methodaccording to any of the preceding claims, characterised in that, afterthe removal of the ferrous metals (8), the slurry (7) is oxidised, forexample aerated.
 9. Method according to any of the preceding claims,characterised in that, after the removal of the ferrous metals (8), thesand fraction (33) is removed from the slurry by means of at least onesand separator (32), for example a hydrocyclone.
 10. Method according toclaim 9, characterised in that the sand fraction (33) is separated asecond time from the organic slurry in a sand separator (34), wherebysaid organic slurry (36) is preferably added to the slurry (37) of thefirst sand separation.
 11. Method according to claim 9 or 10,characterised in that the sand fraction (33 or 35) is dewatered afterthe separation in the sand separator (32 or 34).
 12. Method according toclaim 10 and 11, characterised in that the dewatered sand fraction (33),after the first sand separation in the sand separator (32), is mixedwith water (53) originating from the dewatering of the sand fractionafter the second sand separation in the sand separator (34), which water(53) is preferably treated before the mixing, for example in aphysicochemical manner.
 13. Method according to any of the precedingclaims, characterised in that, after the removal of the ferrous metals(8), a fibrous fraction (41) is removed from the slurry (38).
 14. Methodaccording to the preceding claim, characterised in that this fibrousfraction (41) is removed by sieving it with at least one sieving device(39) with openings which can let particles through whose dimension, atleast in one direction, and preferably in at least two standingdirections, is smaller than or equal to 2 mm.
 15. Method according toclaim 13 or 14, characterised in that, before and/or after the firstseparation of the fibrous fraction (41), there is an additionalseparation of the remaining ferrous metals (48A, 49A) from the slurry(38,40), in particular by means of magnets.
 16. Method according toclaim 14 or 15, characterised in that the separated fibrous fraction(41) is dewatered, whereby the water thereof is preferably carried backto the slurry (40) originating from the separation of the fibrousfraction (41).
 17. Method according to claim 16, characterised in thatdispersed remainders of ferrous metals (58) are removed from the fibrousfraction (41), preferably by means of magnets.
 18. Method according toany of claims 13 to 17, characterised in that the fibrous fraction (41)is further separated into pure fibres (43) and other substances,preferably by means of sieving in a sieving device (42).
 19. Methodaccording to claim 11 or 12 and claim 18, characterised in that thefibres (43) are dewatered and in that the water (63) is added to thewater (56) of the dewatering of the sand fraction (35).
 20. Methodaccording to claim 11 or 12 and claim 18, characterised in that, afterthe dewatering, the fibrous fraction (41) is mixed with water (53)coming from the dewatering of the sand fraction (35).
 21. Methodaccording to any of the preceding claims, characterised in that, afterthe separation of the ferrous metals (8, 48A, 49A), and after thedewatering of the slurry (7, 19, 31, 37, 38 or 40), the obtaineddewatered fraction (21) is subjected to a biological treatment, inparticular to composting.
 22. Method according to any of claims 9 to 12and according to claim 21, characterised in that the sand fraction (35)is added to the dewatered fraction (21) which is biologically treated.23. Method according to any of claims 13 to 20 and claim 21,characterised in that the fibrous fraction (41) or the fibres (43) areadded to the dewatered fraction (21) which is biologically treated. 24.Method according to any of the preceding claims, characterised in thatthe dewatered fraction (21), after the removal of the ferrous metals(8), and possibly the sand fraction (33) and the fibrous fraction (41),and after the dewatering, is treated with a chelator.
 25. Methodaccording to claim 24, characterised in that, after the treatment withchelate, the slurry is dewatered again, and the water of this lastdewatering is treated and added to the dewatered fraction (21) againbefore the treatment with the chelator.
 26. Method according to claims1, 14 and 18, characterised in that the slurry (7) is first sieved witha sieving device (5) which lets particles through of which at least onedimension is smaller than 5 mm and preferably at least two dimensionsare smaller than 5 mm, that the fibrous fraction (41) is removed bysieving with the help of at least one sieving device (39) with openingswhich can let particles through whose dimension in at least onedirection, and preferably in at least two standing directions, issmaller than 1 mm, and in that the fibrous fraction (41) is furtherseparated in pure fibres (43) and other substances, preferably by meansof sieving in a sieving device (42) whose dimension in at least onedirection, and preferably in at least two standing directions, issmaller than 500 micrometer.